The present invention relates to a method of treating thrombocytopenia and a novel indolocarbazole derivative useful as a therapeutic agent for thrombocytopenia. A therapeutic agent for thrombocytopenia is expected to be useful for the treatment of the decrease of blood platelets in number which is a side effect of chemotherapy for cancer and transplantation of bone marrow and for various diseases involving thrombocytopenia.
Decrease of blood platelets in number due to various hematopoietic disorders causes serious symptoms including an increased tendency to hemorrhage. At present, platelet transfusion is considered to be effective against decrease of blood platelets, but an ample amount of blood platelets is not always supplied.
Known hematopoietic factors which stimulate the production of blood platelets include interleukin (IL) 6 and IL 11 (see Blood, 75, 1602 (1990), ibid, 81, 901 (1993)).
Indolocarbozole derivatives having two glycosidic inkages are known to have inhibitory activity against a variety of protein kinase, such as protein kinase C, antitumor activity (see Japanese Published Unexamined Patent Application Nos. 220196/87 (U.S. Pat. No. 4,935,415), 168689/89 (U.S. Pat. No. 4,877,776), WO 88-07045 (U.S. Pat. No. 4,923,986) and WO 89-07105 (EP 383919A)), inhibitory activity against blood platelet agglutination (see Japanese Published Unexamined Patent Application No. 364186/92) or vasodilating activity (see Japanese Published Unexamined Patent Application No. 143877/89) .
Indolocarbozole derivatives with one or no glycosidic linkage are known to have protein kinase C inhibitory activity (see Japanese Published Unexamined Patent Application Nos. 149520/90 (EP 328000A), 294279/91 (EP 434057A) and 174778/90 (EP 370236A), and WO 93-24491), antitumor activity (see WO 93-11145 (EP 545195A)), antiviral activity (see WO 93-18766) , or antithrombotic and antiallergic activity (see Japanese Published Unexamined Patent Application No. 294279/91 (EP 434057A)).
However, it is unknown that indolocarbazole derivatives of either type exhibit stimulating activity on blood platelet production.